the best you can read from the developers on the status of 1.5.3:
https://wiki.scribus.net/canvas/1.5.3_Releasethe release notes.
concerning who is using 1.5.3: most of the people using it do so because 1.5.3 feels better than 1.4.6, even with the few very prominent awkwardness that you will notice as soon as you open it.
not because it has a higher number.
the most important (and visible and very simple) one: the dockable proprieties palette.
personally, there is one rule of thumbs i follow (and suggest other to follow): create a demo document (or small project) to test every new feature before using it in a "real" project.
if you do so, you probably won't get any (or very few) surprises.
and be ready to write bug reports when you hit one: if they are "important" they will be solved rather quickly (mostly a matter of hours).
(of course, i'm talking about bugs in part of the code that are supposed to work correctly, not the bugs in still experimental parts of code)
the boat has sailed, 1.5.3 is stable enough to be used and people are using it.
we had a very similar situation in the 1.3.x branch, long before 1.4 was released... and it's at that time that i've stopped insisting when people want to use the development version during the very long stabilization phase.
and yes, as utnik writes, if somebody goes for the development version, she should keep it update to the latest available code / release... (and keep a backup of the binaries that she knows work for her).
of course, you don't have to make the switch yourself!
but it might be healthier for yourself to often refrain from telling others not to do it...
(in my case it was even "harder", since i did make the swtich, but i was telling other people not to do it : - )